Volatile memories such as Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM) are generally used as a main memory and a cache memory. Owing to their benefits of random access and fast operation, the volatile memories are feasible for storing code and data to be processed in a Central Processing Unit (CPU). However, if power is not supplied to the volatile memories, stored data is erased from the volatile memories, which makes the volatile memories unviable for long-term data storage. Therefore, a non-volatile memory such as a hard disk or a flash memory is used for data storage. Despite impossible random access and slow operation (relative to a volatile memory), the non-volatile memory is suitable for storing a large amount of data permanently.
Non-Volatile RAMs (NVRAMs) have recently been commercialized. The NVRAMs include Phase-change RAM (PRAM), Magnetic RAM (MRAM), and the like. The NVRAM is randomly accessible on a byte basis like the DRAM and also has the non-volatile memory property of permanent data storage.
In other words, while the NVRAM is identical to the DRAM in functional features, the NVRAM preserves data despite power-off. Particularly, the MRAM has a higher integration level per unit silicon area than the SRAM and the DRAM. Therefore, the MRAM is cost-effective. It is expected that the DRAM and the SRAM will give way to the MRAM in view of the advantages of the MRAM.
Although the recent NVRAM will substitute for the DRAM, the NVRAM faces some challenging issues.
The memory cells of the NVRAM are worn out by programming and erasure. As compared to the DRAM that offers an almost infinite number of write operations, the NVRAM allows only a limited number of write operations because the memory cells are worn out due to repeated writes to the NVRAM. The PRAM guarantees about 108 writes, the FeRAM guarantees about 1012 writes, and the MRAM guarantees about 1014 writes.
Wear leveling is a technique of arranging data so that erasures and re-writes are distributed evenly across all cells of a memory by preventing a high concentration of write cycles in specific cells in consideration of the service life of the memory.
A kind of volatile memory, NAND flash prevents excess erasures of a specific memory block by managing blocks and pages through a flash conversion layer, so that every memory block is evenly used. For this purpose, the flash conversion layer records and manages the count of erasures of each block.
If the NVRAM is used as a main memory, instead of the DRAM, this is problematic because the Operating System (OS) and higher application-layer software of a computer system such as an existing portable terminal give no regard to wear leveling.
While the NVRAM ensures relatively high endurance, wear leveling may be considered to prolong the life of the NVRAM in order to substitute the NVRAM for the DRAM.
When the NVRAM is powered off and then powered on, data written on the NVRAM is generally erased. However, some data may still remain on the NVRAM.
If the remaining data is significant information such as a password, the information may risk exposure to an unauthorized third party.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.